Oryzomys baroni Allen, 1897

Prado, Joyce Rodrigues Do & Percequillo, Alexandre Reis, 2016, Systematic studies of the genus Aegialomys Weksler, Percequillo and Voss, 2006 (Rodentia: Cricetidae: Sigmodontinae): Annotated catalogue of the types of the species-group taxa, Zootaxa 4144 (4), pp. 477-498 : 490-492

Oryzomys baroni Allen, 1897

Holotype. AMNH 11820/10112, a female specimen, collected by O. T. Baron, in 27.IV.1894 ( Fig. 6 ).

Type condition. This specimen is preserved as skin and skull, both in good condition; the skin has a small area on the tail that has been torn and sown, and the pes are tied to each other and to the tail; the skull exhibit damaged nasolacrimal capsular projections as well as the proximal portion (maxillary and frontal) of the infra-orbital foramen.

Type material. The description of this species was based also on two additional specimens, AMNH 10111 and AMNH 11819: an old female, with molars and a sub-adult female, with molars only slightly worn, respectively.

Type locality. Malca, Cajabamba, alt. 8000 feet. The more appropriate designation would be Malca, Province Cajabamba, Region Cajamarca, Peru; alt 8,000 ft (circa 2,400m); geographical coordinates of this locality are 07°37’S, 78°03’W. The type locality is represented in figure 3.

Original description. This species was described on the Bulletin American Museum of Natural History, vol. 9, issue 8, 1897:117–118, as follows:

“Above yellowish brown, mixed with many blackish tipped hairs; sides paler and more grayish; below clear whitish gray, the hairs plumbeous at base, the basal portion slightly tinging the surface; fore limbs grayish brown to the base of the toes, which are lighter; lower portion of tarsus dusky, metapodials and toes dull soiled whitish; ears rather large, clothed thinly on both surfaces with short fine hairs, brown externally, slightly rufous internally; tail brown, nearly concolor, being barely lighter below, clothed with fine short hairs, too sparse to conceal the annulations. Mammae, i pectoral, i abdominal=4; only 3 functionally developed in the present specimen.

Skull—Cranial portion rather flat; facial portion broad, with very broad nasals; supraorbital and cranial ridges well developed, forming raised beads; palatal floor extending but slightly behind the last molar, but in other respects the skull and dentition are nearly as in typical Oryzomys , including tooth pattern.”

Original dimensions. Total length: 290 mm; head and body: 130 mm; tail: 160 mm; hindfoot: 30 mm. Ear from notch: 18 mm. Skull: Total length: 35 mm; basal length: 30 mm; zygomatic breadth: 17.5 mm; interorbital breadth: 11 mm; length of nasals: 13.5 mm; width of nasals at middle: 5. 5 mm; interparietal, 10 x 3 mm; length of interpterygoid fossa: 10.3 mm; palatine length, 15mm; length of anterior palatine foramina: 7 mm; upper molar series, 5.3 mm; diastema, 9 mm; length of lower jaw (from inner base of incisors to posterior border of condyle): 19 mm; from incisive tip to condyle: 22.3 mm; height of lower jaw at condyle: 8.6 mm; height of ramus at m1: 5 mm. Other craniodental measurements are in table 2.

Morphological description. Pelage soft, dense, lax, and long; yellowish wool and cover hairs and brown guard hairs; dorsal color yellowish cream, lightly grizzled with brown, resulting in grayish-yellow color; venter grayish; tail longer than head and body length, bicolored dorsoventrally, covered by very long hairs, with very small scales, with approximately 23 scales/cm; pes densely covered by long and white hairs, ungual tufts short and thin, some the same size as claw and others smaller, tufts white; plantar pads fleshy, including thenar and hypothenar; pinnae covered internally and externally with brown hairs with yellowish apex.

Skull moderately robust, with long and broad rostrum (approximately 38% of skull length [LN/ONL ratio]); zygomatic plate greatly projected anteriorly, not reaching beyond nasolacrimal capsule; rostral fossa moderately deep; greatly projected plate and moderately deep fossa, configuring a very deep and wide zygomatic notch; interorbital region convergent anteriorly, with supraorbital margins sharp and acute, forming small dorsolateral crests; zygomatic arches weakly divergent posteriorly, wider near the squamosal root; braincase small and delicate, elongated; braincase with temporal margins slightly squared, without crests; interparietal short and wide; frontosquamosal suture contiguous with fronto-parietal suture; alisphenoid strut absent; anastomotic channel present, configuring pattern 3 of carotid circulation ( Voss 1988); parietals expanding over surface side of skull; incisive foramen long, wider medially, with anterior and posterior margins more acute, posterior margin leveled to the alveolus of M1; posterior margin of zygomatic plate situated anterior to the alveolus of M1; palate intermediate, with mesopterygoid fossa extending anteriorly between the maxillary bones but not between molars; palate with deep posterolateral palatal pits recessed in small and deep palatine depressions; palatal excrescencies absent; anterior border of mesopterygoid fossa rounded, roof of mesopterygoid fossa perforated by large vacuities, occupying the presphenoid and basisphenoid; auditory bulla, with short and wide stapedial process.

Upper incisors opisthodont; upper and lower molars with labial and lingual cusps arranged in opposite pairs; dental series significantly worn, hindering the full dental description.

Observation. Allen (1897) provided a superficial description of the external and cranio-dental morphology, and pointed to the close relationship of this species with O. xanthaeolus . He highlighted, however, that O. baroni specimens are much larger and their coloration is less yellowish than in O. xanthaeolus .

Figures

FIGURE 6. Dorsal, ventral and lateral views of the skull, and lateral view of the mandible of the specimen AMNH 11820 / 10112, holotype of Oryzomys baroni Allen, 1897 (ONL: 35.81 mm).